Field of Invention
The present invention relates generally to a rotor blade pitch control device and, more particularly, to a rotor blade pitch control system that utilizes a plurality of actuators for failure tolerance and system error mitigation.
Prior Art
Flying machines that can takeoff vertically and hover have been around for over a century. To date, the most practical configuration of these machines is the helicopter. Although there have been variations of the helicopter design, all have similar mechanisms. The reasons for the success of the helicopter is the light-weight structural configuration of the rotor system that allows for a low disc loading and the ability to auto-rotate in the event of engine failure.
The helicopter has several limitations, however, including speed and range, because of the rotor's direct exposure to the freestream airflow. Another limitation of the helicopter is the inherent danger of exposed main and tail rotor blades to ground personnel. Finally, noise and airframe vibration is synonymous with the helicopter.
Humans have trying to solve these problems and create a more esthetically pleasing form of the helicopter ever since its creation. An early design conceptualized a propeller housed in a shroud and used a minimum number of vanes for control. See U.S. Pat. No. 1,822,386 (Andersen). Other early designs tried to encapsulate a large rotor with vanes, above and below, to direct flow and provide control. See U.S. Pat. No. 2,777,649 (Williams). Later, single and multi-rotor platforms were studied. See U.S. Pat. No. 2,955,780 (Hulbert). Winged, tandem-rotor platforms were also proposed. See U.S. Pat. No. 2,968,453 (Bright). Piasecki Aircraft Corporation built several prototypes of the wingless, tandem-rotor platforms. They were controlled by using both vanes and differentially adjusting the collective pitch control between each rotor. See U.S. Pat. No. 3,184,183 (Piasecki). More recent designs of the VTOL aircraft have been around for decades without becoming practical. An example of this is the Moller Skycar. The design requires very high power to weight ratios and complex mechanical control systems. See U.S. Pat. No. 5,115,996 (Moller).
Work has continued on the tandem rotor platform vehicle in recent times. These configurations are proposed with wings and without, with gamboling rotors and a multitude of vane configurations. See U.S. Pat. No. 6,464,166 (Yoeli), U.S. Pat. No. 6,883,748 (Yoeli), U.S. Pat. No. 6,892,979 (Milde), U.S. Pat. No. 7,246,769 (Yoeli), U.S. Pat. No. 7,249,732 (Sanders), U.S. Pat. No. 7,857,253 (Yoeli), U.S. Pat. No. 8,651,432 (De Roche) and US. Pat. Appn. Nos. 2009/0084907 (Yoeli), 2010/0270419 (Yoeli), 2011/0049306 (Yoeli), 2011/0168834 (Yoeli). These concepts may have merit for short range and endurance, however, the design is inherently inefficient for both lifting capacity and horizontal flight.